# Test a custom prompt against an already-trained, already-flashed ESP32-S3 model

> Source: <https://gist.github.com/andrisgauracs/e84b842d0f5e301485ecbf6654b0838e>
> Published: 2026-07-31 02:57:35+00:00

| #!/usr/bin/env bash | |
| # esp32-ai: test a custom prompt against an already-trained, already-flashed model. | |
| # Does NOT retrain and does NOT rewrite the 15MB model partition. | |
| # | |
| # Usage: | |
| # ./run_custom_prompt.sh "Once there was a robot" | |
| set -euo pipefail | |
| if [ "$#" -lt 1 ]; then | |
| echo "Usage: $0 \"Your custom prompt\"" | |
| exit 1 | |
| fi | |
| PROMPT="$1" | |
| REPO_DIR="esp32-ai" | |
| if [ -f "$REPO_DIR/pyproject.toml" ]; then | |
| cd "$REPO_DIR" | |
| elif [ ! -f "pyproject.toml" ]; then | |
| echo "Can't find the esp32-ai repo. Run this from the same folder as build_and_flash.sh, after it has cloned esp32-ai." | |
| exit 1 | |
| fi | |
| if [ ! -f "data/bpe32768.json" ]; then | |
| echo "data/bpe32768.json not found. Run build_and_flash.sh at least once first (it trains the tokenizer)." | |
| exit 1 | |
| fi | |
| # ---- Detect port ---- | |
| CANDIDATE_PORTS=(/dev/cu.usbmodem*) | |
| if [ ! -e "${CANDIDATE_PORTS[0]}" ]; then | |
| echo "No /dev/cu.usbmodem* device found. Is the board plugged in?" | |
| exit 1 | |
| elif [ "${#CANDIDATE_PORTS[@]}" -eq 1 ]; then | |
| ESP32_PORT="${CANDIDATE_PORTS[0]}" | |
| else | |
| select choice in "${CANDIDATE_PORTS[@]}"; do | |
| [ -n "$choice" ] && ESP32_PORT="$choice" && break | |
| done | |
| fi | |
| echo ">> Using port: $ESP32_PORT" | |
| # ---- Tokenize the custom prompt with the same tokenizer gen_assets.py uses ---- | |
| echo ">> Tokenizing prompt: \"$PROMPT\"" | |
| TOKENIZE_SCRIPT="$(mktemp /tmp/tokenize_prompt_XXXX.py)" | |
| cat > "$TOKENIZE_SCRIPT" << 'PYEOF' | |
| import sys | |
| from tokenizers import Tokenizer | |
| tok = Tokenizer.from_file("data/bpe32768.json") | |
| prompt = sys.argv[1] | |
| ids = tok.encode(prompt).ids | |
| print(f'prompt "{prompt}" -> {len(ids)} ids: {ids}') | |
| print(f"round-trip: {tok.decode(ids)!r}") | |
| print("static const int PROMPT_IDS[] = {" + ", ".join(map(str, ids)) + "};") | |
| PYEOF | |
| GEN_OUTPUT="$(uv run python "$TOKENIZE_SCRIPT" "$PROMPT")" | |
| rm -f "$TOKENIZE_SCRIPT" | |
| echo "$GEN_OUTPUT" | |
| PROMPT_IDS_LINE="$(echo "$GEN_OUTPUT" | grep -o 'static const int PROMPT_IDS\[\] = {[^}]*};')" | |
| if [ -z "$PROMPT_IDS_LINE" ]; then | |
| echo "!! Couldn't parse a PROMPT_IDS line out of the tokenizer output. Aborting." | |
| exit 1 | |
| fi | |
| echo ">> New prompt line: $PROMPT_IDS_LINE" | |
| # ---- Paste it into the sketch ---- | |
| SKETCH_FILE="firmware/esp32_llm/esp32_llm.ino" | |
| sed -i.bak -E "s/static const int PROMPT_IDS\[\] = \{[^}]*\};/${PROMPT_IDS_LINE//\//\\/}/" "$SKETCH_FILE" | |
| # ---- Rebuild and reflash just the app (model partition untouched) ---- | |
| FQBN='esp32:esp32:esp32s3:UploadSpeed=921600,USBMode=hwcdc,CDCOnBoot=default,UploadMode=default,CPUFreq=240,FlashMode=qio,FlashSize=16M,PartitionScheme=custom,PSRAM=opi,DebugLevel=info' | |
| echo ">> Recompiling firmware with new prompt..." | |
| arduino-cli compile \ | |
| --fqbn "$FQBN" \ | |
| --build-property compiler.optimization_flags=-O3 \ | |
| --build-path /tmp/esp32-llm-uart \ | |
| firmware/esp32_llm | |
| echo ">> Flashing app (model partition is untouched)..." | |
| arduino-cli upload -p "$ESP32_PORT" \ | |
| --fqbn "$FQBN" \ | |
| --input-dir /tmp/esp32-llm-uart firmware/esp32_llm | |
| echo ">> Opening serial monitor. Press the board's RESET button now." | |
| arduino-cli monitor -p "$ESP32_PORT" --config baudrate=115200 |